1. Field of the Invention
The present invention relates to an electric power transmitting device having a pair of coils for transmitting electric power through an inductive coupling.
2. Prior Art
One known electric power transmitting device having a pair of coils is disclosed in Japanese Laid-Open Patent Publication No. 62(1987)-260526.
As shown in FIG. 7A of the accompanying drawings, the disclosed device includes a case 201 having a recess 201a and a case 202 having a projection 202a with a core 205 disposed therein. A primary coil 203 is disposed around the recess 201a and connected to an AC power supply 206, and a secondary coil 204 is connected to a secondary battery 207. When the core 205 is inserted through both the primary coil 203 and the secondary coil 204, the primary and second coils 203, 204 are magnetically coupled intensively to obtain a sufficient efficiency of electric power transmission therebetween. The secondary battery 207 is charged by electric power supplied from the AC power supply 206 through an inductive coupling provided by the coils 203, 204.
It has also been proposed to position the secondary coil 204 within the primary coil 203 for a sufficient efficiency of electric power transmission therebetween, as illustrated in FIG. 7B.
The cases 201, 202 of the conventional electric power transmitting device are however complex since the recess 201a and the projection 202a have to be formed in and on the respective cases 201, 202. The projection 202a on the case 202 requires a sufficient mechanical strength against possible damage due to impacts.
If the case 202 in which the secondary battery 207 is constructed as a grip, then the electric power transmitting device cannot easily be handled since the core 205 or the secondary coil 204 can only be inserted in the axial direction of the primary coil 203. Therefore, the user may tend to feel awkward when trying to magnetically couple the primary and secondary coils 203, 204 and hence to fail to charge the secondary battery 207. Accordingly, the voltage stored in the secondary battery 207 is likely to be used up and not re-charged.